The present invention, in some embodiments thereof, relates to automatic data analysis and, more particularly, but not exclusively, to devices and methods of reading monochromatic representation of data from various distances.
One of the cornerstones of logistics and monitoring is object labeling. The ability to identify efficiently merchandise and manufacturing products allows improving trade, inventory tracking and manufacture processes. One of the most common object labeling methods is using optical machine-readable representation of data, such as barcodes, for labeling. The readers for identifying machine-readable representations generally consist of two main types: flying spot scanners (E. Barkan and J. Swartz, “System design considerations in bar-code laser scanning”, Opt. Eng. 23, 413-420 (1984)) and electronic imagers (D. Tsi, E. Marom, J. Katz, and J. Swartz, “System analysis of CCD-based Barcode readers”, App. Opt 32, 3504-3512 (1993)), Garcia, J., Sanchez, J. M., Orriols, X. and Binefa, X., “Chromatic aberration and depth extraction”, Proc. of IEEE Conference on Pattern Recognition 1, 762-765 (2000), and B. Fishbain, I. A. Ideses, G. Shabat, B. G. “Salomon and L. P. Yaroslaysky, “Superresolution in color videos acquired through turbulent media”, Opt. Letters 34 1025-1036 (2009, and Bulana, V. Mongab and G. Sharma, “High capacity color barcodes using dot orientation and color separability”, SPIE-IS&T, 7254 (2009). Flying spot scanners use a beam that runs across a barcode, whereas electronic imagers analyze and process the entire barcode image captured as a whole. Both types rely on the fact that the barcode is mono-color (black and white mostly) on a white background and color information is irrelevant. The depth of field of such systems is determined by the highest spatial frequency of the barcode.
Several methods have been presented recently to extend the effective depth of field (DOF) of these readers, usually by introducing additional elements, such as masks and/or by modifying conventional lens elements.
For example, extended depth of field for imaging has been achieved using a lens with a focal distance that varies continuously within the lens aperture, such as a logarithmic aspheric, see, for example W. Chi and N. George, “Electronic imaging using a logarithmic asphere”, Opt. Lett, 26, 875-877 (2001). N George and W. Chi, “Computational imaging with the logarithmic asphere: theory”, J. Opt. Soc. Am. A 20, 2260-2273 (2003) and K. Chu, N. George, and W. Chi, “Extending the depth of field through unbalanced optical path difference, App. Opt. 47, 6895-6903 (2008), which are incorporated herein by reference. For various distances, annular portions of the lens are set to provide a sharp image. The remaining part of the lens gives a blurred image so that the captured image has to be corrected, for example by post processing.
Other solutions for extending the depth of field of a reader involve placing coding masks in the optical train. Such solutions require post-processing for reconstruction of high resolution images, see for example A. Levin, R. Fergus, F. Durand and William T. Freeman, “Image and depth from a conventional camera with a coded aperture”, ACM Transactions on Graphics (TOG) 26, Issue 3 (2007) and W. Thomas Cathey and Edward R. Dowski, “New paradigm for imaging systems”, App. Opt. 41, 6080-692 (2002).
Other solutions for extending the depth of field of a reader involve placing phase masks with one or several annular rings creating a phase difference of π in the optical train, see, for example E. Ben Eliezer, N. Konforti, B. Milgrom and E. Marom, “An optimal binary amplitude-phase mask for hybrid imaging systems that exhibit high resolution and extended depth of field”, Optics Express 16, 20540-20561 (2008), and B. Milgrom, N. Konforti, M. A. Golub and E. Marom, “Improved pupil coding masks for imaging polychromatic scenes with high resolution and extended depth of field”, Optics Express, Vol. 18, Issue 15, pp. 15569-15584 (2010) doi:10.1364/OE.18.015569.